Misconception: In an asteroid belt, spaceships have to dodge a fusillade of oncoming rocks.
Actually: If you were in the middle of an asteroid belt, you probably wouldn’t see any asteroids at all.
A popular game in the early days of video games was Atari’s Asteroids. You would maneuver and spin a small triangular spaceship, blasting space rocks to bits until inevitably one of the asteroids smashes you into line segments. (Magically, the asteroids passed through each other unscathed.)
In space, it seemed, one had to continually dodge destruction. That was true in Green Lantern in 2011 and perhaps most memorably in “Star Wars: The Empire Strikes Back.”
With the Millennium Falcon’s hyperdrive conked out and Imperial TIE fighters and star cruisers close in pursuit, Han Solo steers his spacecraft into a thicket of asteroids.
“You’re not actually going into an asteroid field?” Princess Leia asks.
“They’d be crazy to follow us, wouldn’t they?” Han Solo replies.
C3PO, the fussbudget android, helpfully informs Han, “Sir, the possibility of successfully navigating an asteroid field is approximately 3,720 to 1.” (Statistics pedants point out that C3PO should have said, “approximately one in 3,720.”)
“Never tell me the odds,” Han says as the Millennium Falcon swerves past giant rocks left and right, top and bottom. One of the TIE fighters goes kaboom, then another.
Of course, that asteroid field was in a galaxy far, far away, but it was still silly. Asteroids — small, rocky chunks that never coalesced into a planet — would not be that close to one another for a simple reason: If they were big enough and close enough to pose a danger to a spaceship, they would also be banging into each other, themselves reduced to tiny pieces.
That bad science inspired José Luis Galache, an astronomer at the International Astronomical Union’s Minor Planet Center in Cambridge, Mass., to figure out just how likely a spacecraft would get hit by an asteroid. In our solar system, most asteroids, perhaps a billion of them 100 meters or wider, can be found in a circular belt between the orbits of Mars and Jupiter.
He calculated for those billion asteroids that are bigger than a football field, there would be just one asteroid per 110 trillion cubic miles. That means that in a cube 48,000 miles on a side — that’s a volume equal to more than 400 Earths — there would be just one asteroid inside.
NASA takes advantage of this fortunate circumstance every times it sends a spacecraft to the outer solar system.
During nine missions — most recently NASA’s Juno mission on its way to Jupiter, nothing of significance has ever collided with a spacecraft. Of course, there is never a person seated in that spacecraft; the people looking for problems are back on Earth.
S. Alan Stern, the principal investigator for the New Horizons mission to Pluto wrote that when his spacecraft passed through the asteroid belt in 2006, the chance of collision was “almost vanishingly small — far less than one in one billion.”
In other words, one could snooze while flying through the asteroid belt. But that would make for dull movies and easy video games.